Worth knowing · Humectant

Propylene glycol

Also appears on labels as: PG

A synthetic humectant that holds moisture so semi-moist treats stay soft.

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Where it comes from: Petrochemical synthesis.
Why it's in the product: Texture. It exists so a treat feels soft in your hand.
Safety and toxicity: Prohibited in cat food by the FDA after studies showed it causes Heinz body changes in feline red blood cells. Still legal in dog products at low levels, and dogs tolerate it far better.
Interactions and who should be careful: Do not give dog treats containing it to a cat. Vegetable glycerin achieves the same texture with none of this history.

What the research says

The FDA prohibits propylene glycol in cat food after studies showed it causes Heinz body changes in feline red blood cells. It remains legal in dog products at low levels.

Dogs tolerate it far better than cats, but it's a purely textural ingredient. It exists so a treat feels soft in your hand. Plenty of treats achieve that with vegetable glycerin instead.

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General reference, not veterinary advice. Dose, breed, and existing conditions change the answer, so talk to your vet before changing what your pet eats. Think we got this wrong? Tell us and we log it publicly.